Mercury switch



y 1951 c. A. wooDcocK ET AL 2,551,520

MERCURY SWITCH Filed NOV. 9, 1948 [17 17-517 furs C/zaflZas A. Vl oodaoafi & Sherman E ,m maciz iatented May 1, i951 MERCURY swrrcn Charles A. Woodcock and Sherman E. Womack, Springfield, Ill., assignors to. John W. Hobbs Corporation, Springfield, 111., a corporation of Illinois Application November 9,

1 Claim. 1

This invention relates to improvements in a switch. More particularly, this invention has to do with a switch wherein a quantity of mercury acts as a switching means between contact members in a circuit to close or open the circuit when the switch is tilted bodily.

Heretofore mercury switches have been provided which have enjoyed a limited amountof success. However, due to their design or due to the materials used, the average number of successful contacts made by former switches has been in the vicinity of about 275,000 contacts. In some types of installations where repeated contacts are required such performance is entirely unsatisfactory.

The present invention has for its primary object the provision of a mercury switch that is eificient in operation and has the capacity to make many more successful electrical contacts than has been hitherto possible with similar switches.

According to the general features of the present invention, there is provided a mercury switch comprising a cup member, the open end of which is closed by an insulating washer. The cup acts as one contact member in an electrical circuit while a button disposed at the center of the insulating washer acts as another contact member. When the switch is tilted in one direction a quantity of mercury, freely disposed in the cup member, bridges the contact points and closes the circuit. When the switch is tilted in an opposite direction, the mercury moves away from the contact button to open the circuit.

An important object of this invention is to provide a mercury switch in which the quantity of liquid used therein is so proportioned to the size of the switch that the switch will have a long eifective operating life before the mercury is reduced to the extent that the effective closing of the circuit is impaired.

A still further object of the present invention resides in the provision of a mercury switch having an especially designed contacting button which promotes the long life of the switch and efiects closing of the electrical circuit.

A special feature of the present invention is the provision of a mercury switch having both contact members made of commercially pure unalloyed nickel providing maximum efliciency in operation.

Other and further features, advantages and objects of the present invention will be apparent to one skilled in the art from the following de- 1948, Serial No. 59,152

' tailed description taken in conjunction with the accompanying drawing.

On the drawing:

Figure l is an end elevational view of the switch assembly of the present invention;

, Figure 2 is a side elevational view of the switch of Figure 1;

Figure 3 is a vertical sectional view taken substantially on line IIIIII of Figure 1 showing the switch in a tilted position with the mercury therein bridging the contact points to close the electric circuit;

Figure 4 is a fragmentary vertical sectional view similar to Figure 3 showing a modified form of the contact button of the switch assembly;

Figure 5 is a fragmentary vertical sectional view similar to Figure 3 showing still another form of the contact button featured in the switch of the present invention.

As shown on the drawings:

In Figures 1, 2 and 3, the reference numeral indicates generally the switch assembly of the present invention. Such a switch is usually mounted in a suitable bracket which is arranged to tilt, carrying the switch assembly with it. Since the bracket does not constitute part of this invention, it will not be described in detail.

The switch assembly H) comprises a cup 12, the open end of which is closed by a washer I4 made of insulating material. The peripheral edge of the washer I4 overlies the end of the cup l2 and is held thereagainst by a metal cap I6 which is secured on the cup 12, as by a press fit. An annular flange N3 of the cap it abuts the inr sulating washer l4 and presses it onto the cup.

A contact button 25 is secured in a central aperture 22 of the washer l4 having a head 24 overlying the edges of the aperture 22 on one side of the washer and an annular flange 26 which is peened or spun over the edge of the aperture on the other side of the washer. The button 20 has a fiat contacting member 28 against which a quantity of mercury 30, freely disposed in the cup i2, comes to rest when the switch element is tilted, as illustrated in Figure 3.

It will be understood, of course, that when the switch is tilted back to a horizontal position, or inclined in the opposite direction, the mercury 30 will move away from the contact button 20 and break the electrical circuit which has been closed.

A special feature of the present invention is the fabricating of the cup member I 2 and the contact button 28 of commercially pure, unalloyed nickel. It is further to be noted that .00'150 pound of mercury is used in each switch element which has a maximum diameter of .370 inch and a length of .652 inch.

In Figure 4, a modification of the mercury switch of the present invention is shown in which there is provided a contact button 35 having a substantially spherical contact surface 36. In Figure 5 another modification of the switch is shown wherein the contact surface 38 of the contact button 39 is in the form of a cone. It will be understood, of course, that since mercury has a tendency to wet a nickel surface and since electrical switches have a tendency to are when the circuit is broken, each of the three contact surfaces disclosed in the present application, namely, the flat surface, the spherical surface and the conical surface, has its own distinct characteristics in the efficiency with which the circuit is broken.

From the foregoing description it will be recognized that there is provided in this invention a simple, efficient mercury switch. It has been found by actual tests that this switch will successfully contact on an average of 1,300,000 times, using an included total operating angle of and drawing 2.91 amps. at 6 volts. This performance greatly exceeds that obtained by any of the heretofore manufactured mercury switches.

It will, of course, be understood that various details of construction may be varied through a wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claim.

We claim as our invention:

A mercury switch comprising an elongated cup-like casing of unalloyed nickel, an annular washer of insulating material disposed against the open end of said casing and having a central aperture, a cap disposed over said washer in tight engagement with said casing having a flange portion abutting one face of said washer to press it against said casing, a contact button of unalloyed nickel disposed in the central aperture of said casing having a head portion abutting the inner face of said washer and an annular flange abutting the outer face of said washer, said head and flange cooperating to support said button on said washer, and a quantity of mercury freely disposed in said casing, said casing and said contact button being made of a material for conducting electrical current and being disposed at terminal points of an electric circuit, whereby upon tilting of said casing in one direction said mercury will bridge the space between said casing and said button to close the circuit.

CHARLES A. WOODCOCK. SHERMAN E. WOMACK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 21,815 Bear June 3, 1941 783,612 Clark Feb. 28, 1905 1,282,123 Phelan Oct. 22, 1918 1,670,746 Schroeder May 22, 1928 1,919,345 Sinner July 25, 1933 2,227,040 Staley Dec. 31, 1940 2,347,815 Ebert May 2, 1944 2,414,836 Rickmeyer Jan. 28, 1947 

